It is known that supercharging of air supplied to an internal combustion engine by a compressor driven by a turbine rotated by the velocity energy of engine exhaust gases is effective for reducing the fuel consumption and improving the output characteristics of the engine.
A method for controlling the pressure of air supercharged by the compressor is also known in which selected portions of the exhaust gas conduit upstream and downstream of the turbine is connected by an exhaust gas bypass passage, and an exhaust bypass valve is disposed in this exhaust gas bypass passage so as to control the quantity of engine exhaust gases flowing through the exhaust gas bypass passage.
However, due to the fact that the pressure of air sucked into the intake pipe of the engine is generally utilized for the control of the exhaust bypass valve, the known control method has been defective in that the pressure of supercharged air cannot be controlled at the highest efficiency over a wide operation range of the engine.